Optimization of the use of mother liquor in the synthesis of HKUST-1 and their performance for removal of chromium (VI) in aqueous solutions

In this study, copper-benzene tricarboxylic (Cu-BTC), or better known as HKUST-1, was successfully synthesized using the solvothermal method in a solvent mixture of water, ethanol and N,N-Dimethylformamide (DMF). The mother liquor from the first synthesis was reused as a solvent for the subsequent HKUST-1 synthesis for up to four repetitions, cutting back the use of fresh solvent as much as 37 %. The fifth material obtained showed similar thermal stability and specific surface area to that of the first one, even though the surface morphology turned from an octahedral shape in the first material to an irregular shape in the fifth material. The results of the adsorption study on Cr(VI) in aqueous media showed that the first and the fifth materials had adsorption capacities of 91 mg/g and 100 mg/g respectively. Both adsorbents followed a pseudo-second order adsorption kinetics with a Langmuir isothermal adsorption model.